Sea lice infestations in farmed salmon cause significant welfare harm and threaten wild salmon populations, making their management one of aquaculture's most pressing challenges.
Sea lice welfare harm exists at multiple levels. Farmed salmon with heavy louse loads experience the equivalent of having their skin slowly consumed while alive - lesions progress from superficial irritation to deep tissue damage and secondary infection. At the most severe infestations, mortality rates are high. Treatment is also stressful: thermal baths involve exposure to 34-degree Celsius water; mechanical cleaner systems (Hydrolicer, Thermolicer) cause scale loss and physical damage; chemical treatments involve handling and physiological stress. The welfare of cleaner fish - wrasse and lumpfish - has been largely overlooked despite their deployment in millions per year with very high mortality rates from disease and handling.